Assange still has powerful friends, admirers and allies, with substantial resources at their disposal, among them, leading legal minds who'll understand the political, moral and not least legal implications of just handing him over to the Americans without following even a semblance of due process and British law.
So, that isn't gonna happen, handing him over without a legal hearing where him can defend himself properly. I think it'll take a year, at the very least, and during that year, he could even be granted bail, if a court even accepted that the Americans had a legal case against him, and that's by no means a forgone conclusion.
I think Assange should announce that he's going to leave the embassy of his own free will and grab he moral highground. This would be a big story. His supporters could turn up to greet him, en masse. It's far better to be proactive, rather than wait to be bundled out at night into the arms of the Metropolitan Police when no one is looking.